Hi, On 2021-05-30 03:10:26 +0300, Yura Sokolov wrote: > While this result is not directly applied to stock PostgreSQL, I believe > page compression is important for full_page_writes with wal_compression > enabled. And probably when PostgreSQL is used on filesystem with > compression enabled (ZFS?).
I don't think the former is relevant, because the hole is skipped in wal page compression (at some cost). > Therefore I propose clearing page's empty space with zero in > PageRepairFragmentation, PageIndexMultiDelete, PageIndexTupleDelete and > PageIndexTupleDeleteNoCompact. > > Sorry, didn't measure impact on raw performance yet. I'm worried that this might cause O(n^2) behaviour in some cases, by repeatedly memset'ing the same mostly already zeroed space to 0. Why do we ever need to do memset_hole() instead of accurately just zeroing out the space that was just vacated? Greetings, Andres Freund
